1. Field of the Invention
This invention relates to improvements in a back-rest frame of a seat and more particularly to a back-rest frame including side sections each provided with an extended wall portion and a generally U-shaped upper section connecting the side sections.
2. Description of the Prior Art
A variety of back-rest frames for seats such as vehicular seats have been hitherto proposed and put into practical use. One of them is shown in FIGS. 6 and 7. Referring to FIGS. 6 and 7, a back-rest frame 2 includes a generally rectangular 5 pipe frame member 1. Plate members 3, 3 having a generally L-shaped cross-section are welded to the generally vertical portions of the pipe frame member 2 thereby constituting side sections 1a, 1a. The side sections 1a, 1a maintain their necessary strength under the effect of the pipe frame member 2. The plate members 3, 3 are arranged to be provided with a seat reclining mechanism.
Another back-rest frame is shown in FIGS. 8 and 9. Referring to FIGS. 8 and 9, a back-rest frame 4 includes plate members 6, 6 each of which has a generally C-shaped cross-section and serves as a side section 4a. A generally U-shaped pipe member 5 is welded to the upper ends of the plate members 6, 6 to fixedly connect them thereby serving as an upper section 4b. Additionally, a straight pipe member 7 is welded to the lower ends of the plate members 6, 6 to fixedly connect them. The plate members 6, 6 are arranged to be provided with a seat reclining mechanism.
In the above conventional back-rest frames 1, 4, the pipe members 2, 5 and the plate members 3, 6 constituting the back-rest frames 1, 4 are usually made of ferrous alloy such as mild steel or hard steel in order to obtain a sufficient strength.
However, drawbacks have been encountered in the conventional back-rest frames 1, 4 as set forth below. That is, the side sections 1a, 4a to which the seat reclining mechanism is installed cannot have a complicated closed sectional shape or cannot be formed into a pipe shape. Accordingly, it is usual to employ a ferrous alloy as the material of the side sections 1a, 4a. Additionally, the back-rest frames 1, 4 are assembled by connecting the plate members 3, 6 and the pipe members 2, 5 by welding. This increases the number of component parts of the back-rest frame which increases the weight of the same while also requiring troublesome welding operations which increase the cost of the back-rest.